This invention relates to an imaging system, especially an imaging system for imaging electromagnetic radiation in the optical spectral range. The imaging system includes at least one lens element and at least one first and one second optically functional boundary surface through which the electromagnetic radiation can pass. At least the first and second optically functional interfaces can be located either on one or more lens elements. At least the first and second optically functional interfaces have at least, in sections, a cylinder lens geometry or a cylinder lens-like geometry so that these optically functional interfaces each have a direction which lies in the interfaces and along which at least in sections the curvature of the surface is essentially constant. The direction of essentially constant curvature of the at least one first optically functional interface to the direction of essentially constant curvature of the at least the second optically functional interface being aligned roughly perpendicular to one another.
An imaging system of the aforementioned type is known from U.S. Pat. No. 5,844,723. The imaging system described therein is used for focusing the light emerging from the laser diode onto the entry surface of the optical fiber. To do this two cylinder lenses are used with cylinder axes which are perpendicular to one another. The disadvantage in this system is that imaging errors occur because the two cylinder lenses which are crossed to one another cannot be compensated.
The object of this invention is to devise an imaging system of the above-mentioned type in which imaging errors can be largely avoided.
This object is achieved by the features of the invention. It is provided that at least the first and/or at least the second optically functional interface have an aspherical cylinder lens geometry or an aspherical cylinder lens-like geometry. The aspherical cylinder lens geometry can be formed, for example, by an elliptical, hyperbolic or parabolic cylinder section. By choosing the aspherical cylinder lens geometries for the optically functional interfaces of the lens elements, the difference of optical path lengths of the electromagnetic radiation passing through the imaging system is minimized so that planar wave fronts are present after passing through the imaging system.
Imaging systems as depicted in the invention can be used for the entire optical spectral range from the vacuum-UV range into the far infrared range. It is also conceivable in the invention to use imaging systems in the x-ray range as long as the imaging takes place by refractive optically active interfaces.
It is possible in the invention for there to be at least two lens elements, on one of the lens elements there being the first optically functional interface and on the other of the lens elements the second optically functional interface. It is also possible to provide each of the lens elements with two optically functional interfaces. Then, for example, for each of the lens elements the optically functional interfaces opposite one another have cylinder lens geometries with directions of essentially constant curvature, i.e. with cylinder axes which are perpendicular. Alternatively, it is possible to make each of the lens elements such that there are one first or second optically functional interface and one planar inlet and outlet surface opposite it at a time.
In addition or alternatively to the embodiment of the cylinder lens geometries of the first and the second optically active interface as aspherical cylinder geometries, there is the possibility of providing an additional correction element with at least a third optically functional interface which likewise has at least in sections a cylinder lens geometry or cylinder lens-like geometry. This interface has a direction which lies in the surface along which, at least in sections, the curvature of the surface is essentially constant. By means of this additional correction element imaging errors can be eliminated so that the corresponding wave fronts of the electromagnetic radiation passing through the imaging system are corrected or converted into planar wave fronts.
According to one preferred embodiment of this invention, the direction of essentially constant curvature of at least the third optically functional interface is aligned at an angle of roughly 45xc2x0 to the directions of essentially constant curvature of at least the first and at least the second optically functional interfaces. In this alignment of at least the third optically functional interface of the correction element, the imaging errors which are produced by the first and second optically functional interfaces, which are for example perpendicular to one another and which are provided with a spherical cylinder geometry, can be for the most part corrected. Advantageously, it can be provided that the correction element has two third optically functional interfaces opposite one another with directions of essentially constant curvature perpendicular to one another and are aligned preferably at an angle of roughly 45xc2x0 to the direction of essentially constant curvature of the first and the second optically functional interfaces. Here the third optically functional interfaces can be made concave.
As depicted in the invention it is possible to provide at least the third optically functional interface with a spherical or an aspherical cylinder lens geometry. Especially for an aspherical cylinder lens geometry of at least the third optically functional interface of the correction element can the imaging errors caused by the two lens elements be optimally corrected. The aspherical cylinder lens geometry can in turn be formed for example by an elliptical, hyperbolic or parabolic cylinder lens section.
It is possible to arrange the two lens elements and especially in addition the correction element on a common carrier. One such compact embodiment of the imaging system can be used, for example, to focus the light emerging from a laser diode onto the entry surface of an optical fiber.
It is also possible to use the imaging system, for example, in the form of an imaging system housed on a common carrier as a micro objective lens which can be designed to have a very wide angle.
In objective lenses with a very wide angle under certain circumstances, as a result of the correction of imaging errors which is very effective as in the invention, angles of more than 90xc2x0 can be achieved with relatively good quality.
Here, under certain circumstances it can be especially advantageous, instead of lens elements, to use arrays or linear lines of identical lens elements. In addition, instead of correction elements, arrays or linear lines of identical correction elements can be used. Here it is especially advantageous that by using cylinder lenses or cylinder lens-like geometries, rectangular or square lens elements and correction elements can be used so that arrays or linear lines of lens elements or correction elements with much better space utilization or with maximum attainable packing density can be prepared. These linear lines or two-dimensional arrays of lens elements and optically correction elements can be used for CCD cameras or CMOS cameras. It is also possible to use these imaging systems for process observation, for example for observation of welding processes.